The invention relates generally to erosion, corrosion, and abrasion resistant coatings, methods of coating, and coated articles. While the invention has particular application to coatings for use in glassware manufacturing processes it will be understood that it also has application to parts or substrates coated with such coatings and a process for making such coatings.
The prior art includes U.S. Pat. No. 4,564,555 that discloses a coating for imparting corrosion, temperature and abrasion resistant properties to a part which has bonded thereto at least one layer of metal particles. The layer is bonded in a substantially water-insoluble manner to which is adhered a flame sprayed metal or metalloid oxide layer. The second layer that is always applied with a flame spray process.
It is known to employ an electrolytic process to form a hard, corrosion resistant, glassy oxide film on metals as evidenced by the disclosures in U.S. Pat. Nos. 3,832,293 and 3,834,999 (both to Hradcovsky et al); U.S. Pat. No. 4,082,626 (Hradcovsky) and U.S. Pat. No. 4,184,926 (Kozak). These processes are commercially feasible for use in producing a film directly on metals which inherently possess electrolytic rectifiable properties, such as aluminum, magnesium, titanium and other light metals but such coatings have high permeability to gases and liquids.
U.S. Pat. No. 3,248,251 ('251 Allen) issued to Charlotte Allen relates to coating compositions consisting essentially of a slurry of solid inorganic particulate material (especially aluminum) in an aqueous acidic solution containing substantial amounts of dissolved metal chromate, dichromate or molybdate, and phosphate. After application of a coating to the substrate, it is heated to a temperature upwards of about 500.degree. F. until the coating is water insoluble.
U.S. Pat. No. 3,869,293 of Robert J. Brambaugh provides a coating composition similar to the composition of the '251 Allen patent which utilizes as the solid particulate material an alloy comprising aluminum and magnesium so as to further improve the corrosion resistance of the coating.
Electrochemical methods for coating steel surfaces in an extremely short time in a dichromate solution containing phosphoric acid or in a chromic acid solution containing boric acid, borate or phosphoric acid are known. However, such procedures do not produce thick oxide coatings which are capable of withstanding abrasion, erosion and corrosion. U.S. Pat. No. 3,400,058 of Edward C. Ross et al notes the problem of forming a successful coating on iron and steel by electrochemical coating.
In U.S. Pat. No. 2,855,350 to Robert Ernst there is disclosed a procedure for producing an oxide coating on aluminum and aluminum alloys by electrolytic oxidation. The patent notes that the presence of copper and iron ions materially affects some electrolytic baths because the appearance of the ions requires an increase in current density which results in corrosion, that is, burning of the part being oxidized.
In accordance with the conventional techniques employed in molding glass parts such as bottles, jars, and the like, the mold surface is frequently treated with a release material by a process known as swabbing. In accordance with swabbing technique or process, a swabbing composition, comprising a mineral oil carrier and a lubricant such as sulphur and/or graphite, is brushed into the glass forming equipment at intervals of between five and forty-five minutes. The swabbing composition is brushed into the mold to allow the molded glass part to be released from the mold without any marks on it and also to preserve the mold against deterioration during the molding process.
Numerous disadvantages have been encountered in using such swabbing techniques. In the conventional swabbing method, the mold must be polished before the swabbing compound is applied. Such a polishing operation inherently involves the removal of metal from the mold, the useful life of the mold is necessarily reduced as the metal is gradually worn away.
The swabbing procedure results in the production of significant amounts of smoke due to the heat at which the glass molds are operated. As a result, conventional oil swabbing techniques pose significant compliance problems under air pollution control regulations
In addition, the swabbing technique exposes the worker performing the technique to the risk of personal injury. The glass making machinery opens for seconds at a time in the course of the operating cycle. If the operator does not complete the swabbing within those few second he will be maimed by the machinery. The worker is also exposed to health hazards because of the clouds of oily smoke produced in the ambient.
Most of the prior art coatings have utilized one of more coatings of the same homogeneous mixture. Thus, coatings that include a lubricant, such as graphite in the mixture, have the graphite substantially uniformly distributed throughout the mixture. This distribution of the typical lubricant, such as graphite, throughout the entire mixture seriously compromises the strength, erosion resistance and durability of many prior art coatings.
The patents described above disclose various coatings that have been proposed including some that have particular application to a glassware manufacturing process. These coatings have not been wholly satisfactory and the almost universal approach to the problem of release of the glassware in the glassware manufacturing industry is the swabbing technique.
Accordingly, it is a primary object of the present invention to provide a new method for treating glass manufacturing molds.
A related object is to provide compositions for use in accordance with such process.
A further object is to provide a method for treating molds used in manufacturing glass parts which avoids the disadvantages of the prior art swabbing techniques.
The general object of the present invention is to provide a coating to eliminate swabbing of blanks, molds, neck rings, bottom plates, plungers, and other parts utilized in the glassware formation process.
Another object of the invention is to increase the production from any given production machinery by (1) permitting faster operation (more bottles per minute) and (2) reducing non-productive down time.
It is a further object of the present invention to provide a coating that when applied to molds and blanks provides a more even temperature distribution and thus eliminates hot spots within the blank that result in defects in the glassware.
It is another object of the invention to provide a coating that is applied to blanks which will eliminate the need to polish the substrate to facilitate release in the manner required in the prior art swabbing technique.
It is a further object of this invention to provide a coating that will comply with air pollution control standards by eliminating the use of oily swabbing materials that produce significant amounts of scrap when applied to hot glass molds.
Another object of the present invention is to provide an erosion resistant coating that will lessen the wear of the blanks and thus extend the useable life of the blank.
Another object of the invention is to improve the quality of the glassware produced from a given blank by limiting erosion that causes substrate wear and thus results in unsatisfactory glass distribution which results in variations in wall thickness of the glassware.
A still further object of this invention is to provide a durable lubricating coating which will facilitate the quick release of glassware during the forming processes.
Still another object of the invention is to provide a coating that will allow the article on which the coating is applied to be repaired by welding procedures without the need to remove the coating or the need to reapply the coating after the welding procedure is complete.
Still another object of the invention is to provide a coating and a method for applying the coating to an article in a manner that allows the user to control the thickness of the coating on respective parts of the article so that, for example, the distribution of the glass in a glassware manufacturing process will be controlled better.
Yet another object of the invention is to eliminate the personal injuries risks associated with the prior art swabbing techniques.
A further object of the invention is to provide a coating having discrete layers in which the lubritic materials are disposed in a top coat and substantially none of the lubritic materials are disposed in the base coat so that the overall coating has a higher durability, strength, and erosion resistance than would be the case if the lubiritic material were uniformly distributed throughout the entire coating.
An additional object of the invention is to provide a coating that can be polished to meet the finish specifications of particularly exacting applications.